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(#) Duplicate Platform Classes

!!! ERROR: Duplicate Platform Classes
   This is an error, and is also enforced at build time when
   supported by the build system. For Android this means it will
   run during release builds.

Id
:   `DuplicatePlatformClasses`
Summary
:   Duplicate Platform Classes
Severity
:   Fatal
Category
:   Correctness
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   3.0.0 (October 2017)
Affects
:   Gradle build files
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/GradleDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/GradleDetectorTest.kt)

There are a number of libraries that duplicate not just functionality of
the Android platform but using the exact same class names as the ones
provided in Android -- for example the apache http classes. This can
lead to unexpected crashes.

To solve this, you need to either find a newer version of the library
which no longer has this problem, or to repackage the library (and all
of its dependencies) using something like the `jarjar` tool, or finally,
rewriting the code to use different APIs (for example, for http code,
consider using `HttpUrlConnection` or a library like `okhttp`).

!!! Tip
   This lint check has an associated quickfix available in the IDE.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
build.gradle:3:Error: xpp3 defines classes that conflict with classes
now provided by Android. Solutions include finding newer versions or
alternative libraries that don't have the same problem (for example, for
httpclient use HttpUrlConnection or okhttp instead), or repackaging the
library using something like jarjar. [DuplicatePlatformClasses]
    implementation 'xpp3:xpp3:1.1.4c'
    ---------------------------------
build.gradle:4:Error: commons-logging defines classes that conflict with
classes now provided by Android. Solutions include finding newer
versions or alternative libraries that don't have the same problem (for
example, for httpclient use HttpUrlConnection or okhttp instead), or
repackaging the library using something like jarjar.
[DuplicatePlatformClasses]
    implementation 'commons-logging:commons-logging:1.2'
    ----------------------------------------------------
build.gradle:5:Error: xmlParserAPIs defines classes that conflict with
classes now provided by Android. Solutions include finding newer
versions or alternative libraries that don't have the same problem (for
example, for httpclient use HttpUrlConnection or okhttp instead), or
repackaging the library using something like jarjar.
[DuplicatePlatformClasses]
    implementation 'xerces:xmlParserAPIs:2.6.2'
    -------------------------------------------
build.gradle:6:Error: json defines classes that conflict with classes
now provided by Android. Solutions include finding newer versions or
alternative libraries that don't have the same problem (for example, for
httpclient use HttpUrlConnection or okhttp instead), or repackaging the
library using something like jarjar. [DuplicatePlatformClasses]
    implementation 'org.json:json:20170516'
    ---------------------------------------
build.gradle:7:Error: opengl-api defines classes that conflict with
classes now provided by Android. Solutions include finding newer
versions or alternative libraries that don't have the same problem (for
example, for httpclient use HttpUrlConnection or okhttp instead), or
repackaging the library using something like jarjar.
[DuplicatePlatformClasses]
    implementation 'org.khronos:opengl-api:gl1.1-android-2.1_r1'
    ------------------------------------------------------------
build.gradle:8:Error: android defines classes that conflict with classes
now provided by Android. Solutions include finding newer versions or
alternative libraries that don't have the same problem (for example, for
httpclient use HttpUrlConnection or okhttp instead), or repackaging the
library using something like jarjar. [DuplicatePlatformClasses]
    implementation 'com.google.android:android:4.1.1.4'
    ---------------------------------------------------
build.gradle:9:Error: httpclient defines classes that conflict with
classes now provided by Android. Solutions include finding newer
versions or alternative libraries that don't have the same problem (for
example, for httpclient use HttpUrlConnection or okhttp instead), or
repackaging the library using something like jarjar.
[DuplicatePlatformClasses]
    compile group: 'org.apache.httpcomponents',
    ^
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`build.gradle`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~groovy linenumbers
dependencies {
    implementation 'my.indirect.dependency:myname:1.2.3'
    implementation 'xpp3:xpp3:1.1.4c'
    implementation 'commons-logging:commons-logging:1.2'
    implementation 'xerces:xmlParserAPIs:2.6.2'
    implementation 'org.json:json:20170516'
    implementation 'org.khronos:opengl-api:gl1.1-android-2.1_r1'
    implementation 'com.google.android:android:4.1.1.4'
    compile group: 'org.apache.httpcomponents',
        name: 'httpclient',
        version: '4.5.3'
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/GradleDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `GradleDetector.testDuplicateWarnings`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection DuplicatePlatformClasses
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="DuplicatePlatformClasses" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'DuplicatePlatformClasses'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore DuplicatePlatformClasses ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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